If there are two nuts on a threaded rod, to enable the nuts to move, there will be a clearance between the flanks of the thread. Without that clearance it would be impossible to move the nuts along the thread.
Pressing two parts together when they are size and size will not allow relative movement. Hence the need for press forces. For a part to be able to move relative to another, clearance must be present
In fuel injection equipment, there is clearance between the pumping plunger and its bore, albeit of the order of a micron, resulting in a definite force required to overcome friction, even when lubricated by the fuel.
If clearance between nut and thread is large enough there will be rotational (angular ) movement of the thread until the clearance is taken up, before any linear movement takes placer.. This is the backlash, with which we all have to live.
If the nuts are forced apart, each nut will move until the clearance is taken up. If the force is great enough, the nuts and thread will be locked together. If the force is reduced, the time will come when the frictional forces between the male and female threads reduce and can be overcome so that linear movement is possible,
So by exerting a force to separate the two nuts, by means of an adjustable tapered screw, or springs, the force can be regulated until the backlash is reduced to the point where clearances, and frictional forces allow relative movement. How much torque is required to do this will relate to the forces between the two nuts, and the coefficient of friction between nut and threaded rod.
Howard